Electrotherapeutic device



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i -lil H, W. PARKER ELECTROTHERAPEUTIC DEVICE Flled July 30 1937OINOOOOQO Sept. 5, 1939.

Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE ELECTROTIHERAI'EUTICDEVICE Canada Application July 30, 1937, Serial No. 156,515

1 Claim.

My invention relates in general to electrotherapeutic devices and moreparticularly to those of such devices which employ high frequencyalternating current to raise the temperature of the human body.

In such devices as now made, it is the custom to employ some type ofoscillation generator, usualy thermionic, to convert the available lowvoltage commercial power to high voltage, high frequency alternatingcurrent. Such devices are very expensive, as due to the high voltageemployed the condensers used to achieve resonance for the circuits andfor by-passing purposes are costly andthe meter necessary to indicatethe strength of current applied to the patient is likewise veryexpensive, in fact constitutes one of the largest items of expense insuch devices.

It has been determined that the frequency most suitable for the purposesfor which such devices are used is of the order of 50 megacycles and Ihave discovered and successfully demonstrated that for frequencies ofthis order all of the expensive condensers may be omitted and a simple,cheap indicating device substituted for the meter to provide a novelcircuit and arrangement of apparatus which is simple, safe, cheap andfully effective and efficient for the purpose intended.

One of the principal objects of my invention comprises producing aninexpensive Oscillation generator which is fully effective and efficientfor electrotherapeutic purposes.

Another object comprises producing an oscillation generator which, whilesimple and inexpensive, is ruged, reliable and especially adapted forelectrotherapeutical uses.

I accomplish all of the above noted desirable objects and results andothers which will hereinafter be apparent by means of the construction,combination and arrangement of circuits and apparatus which will behereinafter more specifically described with reference to theaccompanying drawing forming a part of this specification and which is adiagrammatic representation of a preferred embodiment of my device.

Referring now to the drawing which illustrates diagrammatically apreferred embodiment of my device, the thermionic tubes l, 2, 3, and 4,each provided with a cathode, a grid, and an anode, are connected asshown in parallel in pairs. The cathodes of tubes l and 2 are connectedin parallel and are energized by the winding It] on transformer 9, theprimary l2 of which is connected as usual through fuses and a switchwith any suitable source of commercial alternating current. Similarly,the cathodes of tubes 3 and 4 are connected in parallel and areenergized by transformer winding I l of transformer 9. The grids oftubes l and 2 are connected together through an inductor or inductance 5which is designed to, in cooperation with the interelectrode capacity ofm the tubes, form an input circuit for the tubes which is resonant tothe frequency of the current generated by the generator. This is of theorder of 50 megacycles. Similarly, the grids of tubes 3 and 4 areconnected together through the inductor 6 which is likewise designed to,in cooperation with the internal capacity of tubes 3 and 4, form aninput circuit resonant to a frequency of 50 megacycles. The grid biasresistors I and 8 connected to the midpoints of inductors 5 and 6,respectively, serve as means for properly biasing the grids with whichthey are associated for proper operation of the generator.

The anodes of tubes l and 2 are connected together through an outputinductor or inductance 15, as are the anodes of tubes 3 and 4. The anodeoperating potential and current are supplied from winding E3 ontransformer fi, one extremity of which is connected as shown to theinput circuit of tubes l and 2, and the other to the input circuit oftubes 3 and 4, while the midpoint is connected through an electric lampl4 to ground. The common return path for the anode current is effectedthrough ground, lamp M, inductor l5, conductors I8 and I9, and highfrequency choke coils l6 and II, which are connected to ground as shown.It will be observed that no tuning condensers are utilized in either theresonant grid input circuits or the anode output circuits. The anodecircuits are made reso nant to the frequency desired, megacycles, byproperly proportioning inductor iii to, in. cooperation with theinternal capacity of the tubes 1 and 2, and 3 and 4, provide anodeoutput circuits which are resonant to the desired frequency. 45

It will be further noted that no by-passing condensers are utilized withthe grid bias resistors 1 and 8, as it has been found for the frequencyused that'there is sufficient capacitance in the coils 5;and 6 to effectthe necessary by-passing for proper functioning of the oscillator. Theradio frequency choke coils l6 and H in the common return of the anodesupply circuit prevent the passage of the high frequency currenttherethrough and confine such current to the load circuit comprising theoutput impedance l5, conductors I8 and I9 and the variable couplerconnected between the applicator pads 26 and 21 and the output impedanceI5, the applicator pads and the patient to whom they are applied. Thevariable coupler shown comprises a pair of metallic plates 22 and 23mounted in fixed relation with their plane surfaces coplanar by means ofthe insulating member 24 and a pair of similar plates 20 and 2| mountedwith their plane surfaces coplanar and for rotation in a plane parallelto the plane of the plates 22 and 23 and maintained in such relativeposition to each other and with plates 22 and 23 by means of theinsulating knob 25. As the knob 25 is rotated plates 20 and 2| arerotated relatively to plates 22 and 23.

As shown in the drawing, the variable coupler is adjusted for maximumtransfer of energy between the output inductor |5 and the applicatorpads 26 and 21. When the plates 20 and 2| are rotated by the knob 25 thetransfer of energy to the load is gradually reduced until a minimum orzero transfer of energy is reached, when the plates 20 and 2| have beenturned through an angle of degrees with respect to that shown in thedrawing. This variable coupler serves as an effective means for varyingthe load current without disturbing the symmetry of the connectionbetween the generator and load and with minimum frequency change, asfully disclosed in my copending application Serial No. 99,221, filedSeptember 3, 1936, Patent No. 2,116,080 dated May 3, 1938.

The applicator pads 26 and.2| are the usual metal back fabric padsemployed in applying electricity to the human body, and no furtherexplanation of such electrodes is deemed necessary. In the operation ofthe device the pads are applied to the desired portions of the patientsbody and the portion of the body included between the pads constitutes aresistance completing the load circuit of the device.

It will be noted that the generator circuit is of the push-pull type andtherefore symmetrical and that tubes and 2 are in one symmetrical halfand tubes 3 and 4 in the other symmetrical half of the generator. Itwill be further noted that the lamp l 4 is included in the common returnconnection of the anode current supply circuit or, that is, the circuitsupplying. alternating current from the source to the generator throughthe transformer 9.

I have discovered and successfully demonstrated that for such agenerator having the desired output of about 500 milliamperes, the lampl4 may preferably be an ordinary volt 60 watt lamp to serve as the soleinexpensive means for correctly indicating the strength of currentsupplied to the generator as determined by the current drawn from theoutput of the load circuit of the generator and thus to eliminate anexpensive meter for thesame purpose. Such a lamp shows no illuminationat all when no current is drawnfrom the load circuit, as the no loadcurrent of the generator is of the order of 200 milliamperes and this isnot sufiicient to heat the filament of the lamp to a visible degree.

At 275 milliamperes load the lamp glows at a dull orange color, and at500 milliamperes, or full load, the lamp glows with a dazzling brightwhite light. The scale of color of the lamp indicating the current inthe load circuit is as follows: 1

Illumination Current in load Milliamperes The scale of a meter forindicating the current strength in the load circuit is linear, while thelight scale is approximately a fourth power relation of the temperatureof the filament. The temperature of the filament is in accordance withthey half power of the current. It is, therefore, apparent that the lampis more sensitive in indication than a meter. The lamp is further ofadvantage as it has been found that, if the patient moves his bodyrelative to the electrode pads, the lamp changes in color, indicatingmore or less heat transfer and as such color changes can be seen acrossthe operating room, the lamp indicator is preferable to a meter becausesuch electrical treatments are generally applied to several patients inthe same room and the condition of each patient can be noted by oneoperator. The overload characteristic of the lamp in flashing as thepatient moves and the fact that the lamp burns out without noise orsmoke in case of exreme overload is important in that it saves theoscillator tubes from overload and does not startle the patient. Iprefer to employ a lamp of the incandescent filament type rather than agaseous discharge type such as a neon lamp because the filament lampshows no illumination for the no load current of the generator.

It will be noted that the oscillation generator circuit is of the typegenerally referred to as selfrectifying in that each symmetrical partoscillates alternately, that is, as the cathodes of one pair of tubesare energized by a negative half wave of alternating current andconsequently the anodes of the same tubes have impressed on them apositive half wave that particular pair of tubes oscillate while theremaining pair do not oscillate; thus, each pair of tubes oscillatealternately to produce in the output inductor l5 a substan-' tiallycontinuous high frequency current. It will be further noted that thetubes in each symmetrical half of the oscillator are provided withindependent cathode energizing circuits; that is, transformer windingsl0 and M, respectively. This allows the cathodes of the tubes to have apotential different from ground potential-and permits the grounding ofthe anode circuit as shown for the sake of safety and to protect thepatient from shocks.

It Will be observed from the foregoing that my improved device comprisesa minimum number of inexpensive parts and is consequently simple,inexpensive, rugged and reliable. It will be 0-bservedthat there are noexpensive condensers or meters employed and that, as the cathodes areindependently energized, the output and anode supply circuit maybegrounded and the device thus be made safe to operate. I

While I have illustrated and completely described by way of example,only one embodiment of my device, it will be apparent that numerouschanges in details may be made therein without departing from the spiritor intended scope of the invention. 1 do not, therefore, desire to limitmyself to the foregoing except as may be pointed out in the appendedclaim in which I claim:

An oscillation generator for electro-therapeutic use comprising, twopairs of two thermionic tubes each, input and output circuits connectingthe tubes in said pairs symmetrically with respect to each other, a loadcircuit common to said two pairs of tubes, a source of alternatingcurrent for energizing said tubes, a transformer one winding of which isconnected to said source, separate windings on said transformer forseparately energizing the cathodes of each symmetrical pair of saidtubes whereby the cathodes of said tubes may have a potential differentfrom ground potential to permit of the grounding of the anode circuitsof said tubes for the sake of safety and to protect the patient fromshocks, an additional winding on said transformer connected to theanodes of said tubes and including a connection common to said anodes,said common connection including a tuned impedance connected between theanodes of the tubes in each pair of said tubes whereby each pair oftubes operates alternately to generate oscillations during positive halfcycles of the alternating current from said source and said commonconnection being grounded and including an indicating device forindicating the strength of current supplied to said oscillationgenerator as determined by the current in said load circuit.

HENRY W. PARKER.

